If you have any comments on this booklet or the National Fetal Anomaly Screening Programme, please write to: NSCFASPMP07/07 Telephone ordering: 0870 1555455 Only NHS staff can reproduce any information in this booklet freely. Antenatal and Newborn Screening Programmes Provided by the National Programme Centre NHS Fetal Anomaly Screening Programme UK National Screening Committee Unit G1, The Innovation Centre, University of Exeter, Rennes Drive, EXETER EX4 4RN Screening for Down’s syndrome in Multiple Pregnancy When you are expecting twins, triplets or more July 2007
Transcript
If you have any comments on thisbooklet or the National FetalAnomaly Screening Programme,please write to:
NSCFASPMP07/07Telephone ordering: 0870 1555455
Only NHS staff can reproduce any information in this booklet freely.
Antenatal and NewbornScreening Programmes
Provided by the National Programme CentreNHS Fetal Anomaly Screening ProgrammeUK National Screening CommitteeUnit G1, The Innovation Centre, University ofExeter, Rennes Drive, EXETER EX4 4RN
Screening forDown’s syndromein MultiplePregnancy
When you areexpecting twins,triplets or more
July 2007
Page Sectionnumber
04 What is Down’s syndrome?
05 What causes Down’s syndrome?
06 Diagnosis of a multiple pregnancy
06 How identical (monozygotic) and non identical (dizygotic) twins arise
09 How common is Down’s syndrome in multiple pregnancy?
09 Testing for Down’s syndromeduring pregnancyWhat is a screening test?
10 What is a diagnostic test?
Should I have the screening test for Down’s syndrome?
11 What screening is recommended for a multiple pregnancy?
12 What happens if I decline Down’s syndrome screening?
What happens if I am too late for a nuchaltranslucency scan?
13 What happens next if I have a higher risk result and I am offered a diagnostic test?
Contents
Page Sectionnumber
14 Diagnostic tests for Down’s syndromeWhat can you tell me about diagnostic tests?
What is chorionic villus sampling?
Are there any risks with chorionic villus sampling?
15 What is amniocentesis?
Are there any risks with amniocentesis?
Are these procedures painful?
16 How long does it take to get the results?
How will I get my results?
17 What are the possible results from diagnostic tests?The babies do not have Down’s syndrome
One baby has Down’s syndrome
18 Both babies have Down’s syndrome
20 Further information and contact details
23 References
Screening for Down’s syndrome in Multiple Pregnancy
Screening for Down’s syndrome in Multiple Pregnancy
All pregnant women are now offered tests for Down’s syndrome. This booklet gives you some information about Down’s syndrome and testing for it when you are expecting twins, triplets or more, so you can decidewhether to have the tests.
The screening process is different in multiple pregnancy andthe booklet explains this in more detail.
Choosing whether to have the tests is an important decision,for you and for your babies. You need to make the decisionthat is right for you.
04
Down’s syndrome have learning difficulties. Some havemore serious difficulties than others.
It is hard to tell in babies how much they will be affectedas children, or when they are grown up. Some adultswith Down’s syndrome are able to get jobs and livefairly independent lives.
However, most people with Down’s syndrome needlong-term help and support.
A number of health problems are linked to Down’ssyndrome. But again, people vary, and some peoplewith Down’s syndrome enjoy good health. Problemswhich are linked with Down’s syndrome include heartproblems and reduced hearing and vision. Many ofthe problems can be treated, and frequent healthchecks can make sure that any problems are pickedup as early as possible. Most people with Down’s syndrome live to be 50 years of age and some live tobe over 70. Alzheimer’s disease (a form of seniledementia) may affect people with Down’s syndromeat an earlier age than other people.
What causes Down’s syndrome?
Inside all the cells of our bodies are tiny structurescalled chromosomes. These chromosomes carry thegenes that determine how we develop. Most people
05
What is Down’s syndrome?
There is no such thing as a typical person withDown’s syndrome. Like all people, they vary a lot inappearance, personality and ability. People with
Screening for Down’s syndrome in Multiple Pregnancy
06
One of the first things to be looked at is whetheryour twins have one or two placentas, and whetherthey might be identical (monozygotic) or non identical(dizygotic or fraternal). This is called establishing thechorionicity.
Whether the babies are identical or non identical,and whether they share one placenta, is veryimportant in understanding your options forDown’s syndrome screening.
Identical Twins
Identical twins are also known as monozygotic (MZ)because they come from a single fertilised egg (zygote)which divides. The two babies will be the same sex andboth will have the same genes.
Non Identical twins
Non identical twins are known as dizygotic (DZ) orfraternal. They come from two separate eggs beingfertilised by two separate sperm. Non identical twinsare genetically no more alike than other single bornbrothers and sisters and they can be either the samesex or a boy and girl.
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have 23 pairs of chromosomes in each of their cells.When our bodies produce the special cells needed tomake babies, the chromosome pairs divide and rearrangethemselves. Sometimes these pairs of chromosomes donot divide correctly, and this causes the baby’s cells tohave an extra copy of chromosome number 21. Thiscauses Down’s syndrome (and is the reason why oneof the medical names for Down’s syndrome is Trisomy21). The extra chromosome cannot be removed fromcells, so there is no cure for the condition.
Diagnosis of a multiple pregnancy
You will have been told that you are expecting twins,triplets or more at your first ultrasound scan.
How identical (monozygotic) and non identical(dizygotic) twins arise:
Monozygotic twins1Sperm
Dizygotic twins - same sex Dizygotic twins - different sexes
The Origins of Dizygotic and Monozygotic Twins
1 Ovum
1 Embryo
2Sperm
2 Embryo
2 Ovum
2Sperm
2 Embryo
2 Ovum
If the fertilised egg divides around 0 to 4 days after fertilisation the babies will each have their own placenta(afterbirth). There will be two inner sacs (amnions) andtwo outer sacs (chorions). This may be written in your
notes as DCDA (Di Amniotic Di Chrionic).
If the division happens around 4 to 8 days the babies will share a single placenta. There will be one outer sac
but each will have its own inner sac and waters (amniotic fluid). This may be written in your notes as
MCDA (Mono Chorionic Di Amniotic).
If the division happens around 8 to12 days the babies will share one inner sac, one outer sac and are both in the same water. This will be written as MCMA
(Mono Chorionic Mono Amniotic).
Screening for Down’s syndrome in Multiple Pregnancy
08 09
How common is Down’s syndrome in multiple pregnancy?
If they are non identical, then the risk of Down’s syndrome for each baby individually is the same as fora single baby. This is around 1 in 800 pregnancies. If theyare identical (monozygotic), because the twins have thesame genes, the risk to both of having Down’s syndromeis the same as if you were having a single baby.
Around 2% of pregnancies affected by Down’s syndrome are twins.
As explained above, the majority of twins with two placentas are non identical but some (approximately onethird) of identical twins can also have two placentas.
What is a screening test?
A screening test is a test offered to all women that carries no risk of miscarriage. The test is usually a scan, ablood test, or a combination of both, that will give a riskor chance of the baby or babies being affected byDown’s syndrome. The result is usually expressed as“higher risk” or “lower risk”. Sometimes a number is
Testing for Down’s syndrome during pregnancy
Separateplacentas
2 inner sacs 2 outer sacs
Fused placentas
2 inner sacs2 outer sac
Single placenta
2 inner sacs 1 outer sac
Single placenta
1 inner sac1 outer sac
Separateplacentas2 inner sacs2 outer sacs
Placentation of twins
Fusedplacentas2 inner sacs2 outer sacs
Singleplacenta1 inner sac2 outer sacs
Singleplacenta1 inner sac1 outer sac
Monozygoticor Dizygotic Monozygotic
This booklet gives the main facts, and tells you how you can get more information if you want toknow more.
You may find it helpful to read through the wholebooklet and consider how you might feel, and whatyou might wish to do, if one baby should be foundto have Down’s syndrome, before making a decision.
What screening is recommended for a multiple pregnancy?
Blood tests alone to screen for Down’s syndrome arenot currently recommended for multiple pregnancies,because markers in the blood are affected by the presence of more than one baby.
The screening test recommended when a mother has a multiple pregnancy should include a specialultrasound examination called a “NuchalTranslucency scan”, which can only be donebetween 11 weeks to 13 weeks and 6 days. Theamount of fluid lying under the skin at the back ofeach baby’s neck is measured. A computer programme uses the measurement, the length ofthe baby (Crown rump length, CRL) and the mother’s age to work out the risk for Down’s syndrome for each baby. It is sometimes known as
Screening for Down’s syndrome in Multiple Pregnancy
11
given, such as 1 in 300, which means that for every300 women with the same risk as you, one will havea baby with Down’s syndrome. Your midwife or doctor will explain your result in more detail with you.
What is a diagnostic test?
A diagnostic test is a test which involves a procedurebeing carried out such as a chorionic villus samplingor an amniocentesis. These tests are described inmore detail later in the booklet. These tests are theonly way to find out for definite if your baby orbabies are affected by Down’s syndrome.Unfortunately, all diagnostic tests carry a risk of miscarriage, and this risk is higher in multiple pregnancies. Your midwife or doctor will explain this toyou in more depth and will decide which of the testsis more suitable for you. These tests are not offeredto all women because of the risks involved, and youshould think carefully before undergoing them.
Should I have the screening test for Down’s syndrome?
Only you can decide that. Some women want to find out if their babies have an increased risk ofDown’s syndrome, and some do not. Informationabout the test and how it works can help you makeup your mind.
10
13
Screening for Down’s syndrome in Multiple Pregnancy
12
the NT test. The results of the NT test may be used incombination with results from a blood test and themother’s age, to calculate the risk of each baby beingaffected by Down’s syndrome.
If you have become pregnant using donated eggs, it isthe approximate age of the woman who donated theeggs which will be needed to calculate the risk for your babies.
What happens if I decline Down’s syndrome screening?
If you decline screening, your care will not be affectedand will continue as routine antenatal care. You will beoffered an anomaly scan at around 18 - 20 weeks. This screening test is a detailed ultrasound scan but itcannot detect Down’s syndrome in your babies. If any abnormalities are seen on this scan, you may beoffered a diagnostic test or referral to a specialist unit ifyou wish.
What happens if I am too late for a nuchal translucency scan?
If you are too late for your nuchal translucency scan(more than 13 weeks and 6 days) it will not be possible to accurately assess each baby’s individual riskof Down’s syndrome.
What happens next if I have a higher risk resultand I am offered a diagnostic test?
Your midwife or doctor will discuss the results withyou and answer any questions that you have. If youhave a higher risk result, you will be offered a diagnostic test which would tell you definitely whethereither of the babies has Down’s syndrome or not.
If you decide to have a diagnostic test, you should bereferred to a specialist fetal medicine unit where thestaff have specialist experience in looking afterwomen with multiple pregnancies.
A specialist in the unit will discuss your care and giveyou advice on which diagnostic test is appropriate foryou. You will have time to make up your mind aboutwhat to do next.
You have two options:
You can decide not to have a diagnostic test. The other option is to have the diagnostic test,knowing this may have other implications whichyou will need to think carefully about, and whichcarries an increased risk of miscarriage.
If you need any further information please refer tothe organisations at the back of this booklet.
What is amniocentesis?
Amniocentesis can be performed from 15 weeks of pregnancy. Under continuous ultrasound guidance afine needle will be inserted through your abdomen,and a sample of fluid surrounding each baby (amniotic fluid) will be taken. The fluid contains cellsfrom each baby, which will be examined in the laboratory. Very occasionally samples do not producea result because the cells do not grow or the resultsare not clear. If this happens, you will be offered asecond amniocentesis.
Are there any risks with amniocentesis?
There is a 2.5% risk of miscarriage in twin pregnancies.This means that for every 100 women who haveamniocentesis, 2 or 3 will miscarry.
Are these procedures painful?
Many women find the procedures uncomfortable butthey should not be painful. You will be advised totake things easy for a day or two afterwards. If possibleyou should avoid activities that involve lifting, bendingor stretching. You may have some discomfort in yourlower abdomen for a day or two after the procedure.This is normal and you can take paracetamol torelieve the discomfort.
15
What can you tell me about diagnostic tests?
There are two diagnostic tests, amniocentesis andchorionic villus sampling. All diagnostic tests in a multiple pregnancy should be done in a fetal medicineunit. This is so that a detailed scan can be performedto accurately identify each baby’s position prior toundergoing any diagnostic test.
What is chorionic villus sampling? (CVS)
CVS can be performed from 11 weeks and at anytime during pregnancy. An ultrasound scan is usedto guide a fine needle through your abdomen orthrough your vagina. A small sample of tissue istaken from the placenta of each baby. The sample is analysed in the laboratory in the same way as an amniocentesis. However, if thebabies share one placenta, only one sample will be taken as the babies will both have the samechromosomes.
Are there any risks with chorionic villus sampling?
There is a 3-4% risk of miscarriage in twin pregnancieswhich means for every 100 women who have the test,3 or 4 will miscarry.
Screening for Down’s syndrome in Multiple Pregnancy
14
Diagnostic tests for Down’s syndrome
How long does it take to get the results?
It can take up to 14 days to get the results of diagnostic tests. Some hospitals offer new “molecular” tests as part of the diagnostic test. These are usually known by their initials – PCR. These tests provide some information within two tothree days, but you will still have to wait up to 14 days for the full diagnostic result. Waiting for the results can be an anxious time, so do call yourmidwife or one of the support organisations listed atthe end of the booklet, if you need to talk.
How would I get my results?
Before you have the diagnostic tests done, your midwife or doctor will discuss how you want toreceive the results.
What are the possible results from diagnostic tests?
Screening for Down’s syndrome in Multiple Pregnancy
16
The babies do not have Down’s syndrome
This is the result that most women get. Some womenare happy just to get this news. They do not want totalk about tests and test results any more. Otherwomen want to discuss the results with somebody.They want to know how the two tests they have had– the screening test and the diagnostic test – canseem to say different things.
We explained earlier that we use screening tests todecide who should be offered a diagnostic test.
When a woman has a diagnostic test and the resultshows that one or both babies, if both are tested,do not have Down’s syndrome, the woman’s earlierscreening test result is sometimes called a ‘false positive’ result. If this happens and you feel confused or upset about it, please talk to yourmidwife of doctor.
One baby has Down’s syndrome
A small number of women who have a diagnostictest will learn that one baby has Down’s syndrome
17
What are the possible resultsfrom diagnostic tests?
Screening for Down’s syndrome in Multiple Pregnancy
and the other is not affected. They then have the following options and it is entirely their decisionwhich one to choose.
� Some people will decide to continue with thepregnancy, make plans and prepare for any challenges they might face, bringing up one twin with Down’s syndrome.
� Some people may feel unable to bring up the child themselves and consider adoption.
� Other people will decide they do not want to continue with the pregnancy and have a terminationof the whole pregnancy.
� Others will decide that they want to consider the procedure to terminate the affected baby with the procedure called “selective termination (feticide)”, which can be discussed in detail with the fetal medicine specialist.
Both babies have Down’s syndrome
A very small number of women who have a diagnostictest will learn that both babies have Down’s syndrome.These women have the following options and it is upto them which they choose.
� Some people will decide to continue with the
18 19
pregnancy, make plans and prepare for any challenges they might face bringing up two children with Down’s syndrome.
� Other people will decide they do not want to continue with the pregnancy and have a termination of the pregnancy.
�Others may feel unable to bring up both children themselves and consider adoption.
� Other chromosomal abnormalities may be detected by diagnostic test, and these will be discussed with you prior to the test being carried out, so you can decide if you wish to receive this information or not.
If you are faced with these results, you need to makesure you reach the right decision for you. You will begiven information and support to help you make yourdecision, but it is up to you to decide what will bebest for you. You will have the opportunity to discuss your options with health care professionals,and you will also be offered information and supportfrom outside the health service. You will have time todecide what to do and will be supported by your GP,midwife and obstetrician in your decision. For furtherinformation please refer to the contact details at theback of this booklet.
� Twins and Multiple Births Association (TAMBA)Website: www.tamba.org.ukTelephone: 0870 770 3305Twin line: 0800 138 0509 (Everyday from 10am to 1pm, 7pm to 10pm)
You can get more information about Down’s syndrome from the following organisations.
20 21
You can get more information about multiplebirths from the following organisations:
� Down’s Syndrome Medical Interest GroupWebsite: www.dsmig.org.ukTelephone: 01159 627 658 extension: 45667An information service for healthcare professionals
Your midwife should have details of any local support groups.
You can get more information about screening from the following organisations.
Screening for Down’s syndrome in Multiple Pregnancy
Your notes
22
• Multiple Births Foundation• Twins and Multiple Births Association• Queen Charlotte’s Hospital, London• Addenbrookes Hospital, Cambridge• St Mary’s Hospital, London • National Down’s syndrome screening programme
This booklet has been written by the NationalDown’s Syndrome Screening Programme MultiplePregnancy Information Group.
Your midwife’s contact details
Name:
Address:
Phone number:
Your doctor’s contact details
Name:
Address:
Phone number:
23
Weisz, B., Pandya, P., Dave, R., Jauniaux, E., (2005),Scanning for Chorionicity ; comparison betweensonographers and perinatologists, PRENATAL DIAGNOSIS,Volume 25, September 2005, pp 835 – 838.
National Down’s Syndrome Cytogenetic Registerwww.wolfson.qmul.ac.uk/ndscr
UKNSC (2004) Testing for Down’s syndrome in pregnancy, National Down’s syndrome screening programme, NHS Publications.
HTA (2003), First and second trimester antenatalscreening for Down’s syndrome, the results of theSURUSS study, Health Technology Assessment, Vol 7,No 11, (www.ncchta.org).
One of the aims of the screening programme is to make sure that it meets set quality standards and guidance. To do this, hospitals may need to use information about yourscreening choices to help improve the programme and to tell NHS planners about anyextra funding they need. We will store personal information under the Data Protection Act1999. By law all NHS staff must follow the act and keep your information confidential.We will only keep your personal information for as long as it is necessary for monitoring thescreening programme. We will not give it to anyone outside the NHS. If you want to discussany concerns you have about how we will keep the information, please ask your midwife.
References
Data protection and guaranteeing quality in the Down's syndrome screening programme.
